The use of premetered and prepackaged portions of ground coffee for the preparation of coffee of the filter type (percolation under atmospheric pressure and under just the effect of the column of hot water placed above the bed of coffee) or of the expresso type (extraction pressure above 0.5 bar and up to 20 bar) has the advantage of making the operations of preparing the coffee easier, while guaranteeing a relatively constant quality of the product.
Currently, these portions are in two main forms. According to a first version, the portion described in U.K. Patent Application Publication No. GB 2,121,762 consists of a sachet package with a nozzle intended to be perforated in order to enable liquid to be injected into the package. The liquid, after extraction through the bed of coffee, drains away through the tear, automatically produced under the effect of the pressure or by mechanically cutting, in the bottom of the package.
The GB '762 sachet package, requiring the presence of a nozzle, is complicated and expensive to produce and to use. The extraction device is also very complicated and requires the device for introducing the aqueous fluid to interact in a sealed manner with the package.
According to a second version, described in PCT Patent Application Publication No. WO 92/0775, the portion consists of a sealed cartridge which is opened by an extraction device under the effect of the introduction of the extraction fluid after being deformed against sharp points. This cartridge consisting of a sealed envelope forming a side wall and two walls of which one constitutes the bottom of the cartridge and the other seals off the opposite end of the cartridge, has the drawback of employing various packaging materials, some of them being sufficiently thick to impart semi-rigidity to them, and can be used only in one sense with an extraction device perfectly matched to the capsule and to its arrangement. This device comprises, towards the upper face of the cartridge, a device for introducing water and, towards the lower face, a device for perforating the bottom of the cartridge, the cartridge having to be clamped, in a perfectly sealed manner, around its entire edge between the two removable parts of the extraction device.